A pressure reactive piston (PRP) situated in a cylinder of an engine may comprise a two-piece piston, wherein the two-piece piston includes a piston crown and a piston trunk. By integrating a separately actuated piston crown with a piston trunk, peak cylinder pressures may be reduced at higher loads without an additional control device. As such, the engine may operate at a higher compression ratio during lower load conditions, and may operate at a lower compression ratio during higher load conditions. Thus, peak temperatures and pressures within the combustion chamber may be reduced.
An example pressure reactive piston assembly is described by Brevick et al. in U.S. Pat. No. 5,755,192. Herein, the pressure reactive piston assembly includes a trunk portion, a crown portion slidably mounted upon the trunk portion, and a resilient element. The resilient element extends between an interior surface of the crown portion and an upper surface of the trunk portion and exerts a force to separate the crown portion from the trunk portion. In particular, the resilient element consists of four sets of Belleville springs.
The inventors herein have recognized potential issues with the approach identified above. The Belleville spring sets included in the pressure reactive piston assembly may have a higher mass than desired. Further, the Belleville springs may have an uneven stress distribution. Further still, Belleville springs may not deflect as desired during certain loads. Specifically, spring rates of Belleville springs may not be suitable for the desired application in a PRP. As a result, there may be an increased risk of knock and reduction in engine efficiency and fuel economy.
The inventors herein have recognized the above issues and developed an approach to at least partly address the above issues. In one example approach, a system is provided including a piston crown, and a spring positioned within the piston crown, the spring including a first ring, a second ring comprising a plurality of apertures, a rolling element positioned within each of the plurality of apertures, and a third ring, wherein the first ring, the second ring, and the third ring are arranged concentrically with the second ring positioned between the first ring and the third ring. In this way, a spring with lower mass may be used within a pressure reactive piston.
For example, an engine may include a cylinder with a pressure reactive piston. The pressure reactive piston may include two distinct pieces: a trunk portion and a crown portion, coupled to each other mechanically. Further, a hoop spring may be positioned within the crown portion of the piston and may rest atop the trunk portion of the piston. The hoop spring may include a first ring, a second ring, and a third ring arranged in a concentric manner. The second ring may include a plurality of apertures with each aperture including a rolling element. The first ring and the third ring may be made of steel, while the second ring may be made of a polymer material. As such, the engine may function with variable compression ratios as the crown portion of the piston slides over the trunk portion of the piston and compresses the hoop spring.
In this way, a hoop spring housed within a two-piece pressure reactive piston may provide variable compression ratio to the engine. By forming the spring of three distinct lightweight elements, a mass of the hoop spring may be reduced. The reduced mass of the hoop spring can lower the weight of the two-piece pressure reactive piston, improving engine performance. Moreover, the hoop spring may experience more uniform stress distribution, thereby increasing durability. Overall, engine efficiency may be improved while enhancing fuel economy.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. Finally, the above explanation does not admit any of the information or problems were well known.